Gums are either hydrophobic or hydrophilic substances of molecular weight ranging from 10,000 to 50,000,000 Daltons, that in an appropriate solvent produce gels or highly viscous suspensions or solutions at low dry substance content. Gums commonly used in food, medicine, and industrial products include starches, cellulose derivatives, pullulan, agar, aloe, gellan, guar gum, locust bean gum, pectin, algin, carrageenan, xanthan, beta glucan, and gum arabic (see Whistler, R. L. (1993) Industrial Gums: Polysaccharides and their derivatives Eds. Whistler R L and BeMiller J. N. (Academic Press) pp 2).
Glucans are homopolysaccharides consisting only of glucose. However, since it is possible to link the glucose molecules in different stereochemical conformations, glucans are a diverse group of compounds with differing chemical, physical, and functional properties.
Chemical structures of polysaccharides are of prime importance in determining their properties. This can be appreciated by comparing the common properties of some common homoglucans. Thus, cellulose, a (1-4)-β-D-glucan, is water insoluble and highly crystalline compared to other polysaccharides. Amylose, a (1-4)-α-D-glucan, is sparingly soluble in water, crystallizes less well than cellulose, and can form rigid thermo-reversible gels. Dextran, a (1-6)-α-glucan, with a small degree of branching, is extremely water soluble and non-gel forming. (See Dea, I. C. M. in (1993) Industrial Gums: Polysaccharides and their derivatives Eds. Whistler R L and BeMiller J. N. (Academic Press) pp 21.).
Oat β(1-3) β(1-4) glucan is classified as a viscous gum, (see Wood, P J (1993) Oat Bran Ed P J Wood (American Association of Cereal Chemists, Inc. St. Paul, Minn.)). Cereal β(1-3) β(1-4) glucan are structural polysaccharides present in the cell wall of cereals as barley and oat, among others.
Oat β(1-3) β(1-4) glucan is recognised by the U.S. FDA as an agent that may aid the prevention of heart disease. In 1997, the FDA allowed oat products to make a health claim. It is important to note that no other beta glucan source, yeast, fungal, bacterial, or cereal are recognised as having these effects and makes an important point that it is the view of those skilled in the scientific and medical art that beta glucans are distinct and a structure function relationship exists.
Unmodified oat β(1-3) β(1-4) glucan forms highly viscous solutions in water at concentrations >0.75%. At concentrations >1.2% the solutions have the consistency of a thick hydrogel.
Glucans of significantly different molecular structure and with different physical and chemical properties compared to oat are found in yeast, fungi, and certain bacteria and genetically engineered bacteria. For example, gellan, polymeric (1-3)β-D-glucopyranosyl [β(1-3) glucan] produced in Alcaligenes faecalis is found in Curdlan J (Takeda Chemical Ind. Ltd.), β(1-4) α(1-6) glucopyranoside produced in Aureobasidium pullulans found in pullulan, and β(1-3) β(1-6) glucopyranoside found in yeast.
The molecular weight of the glucans varies with source. Table 1 shows the average molecular weight of typical gums.
TABLE 1Typical Molecular Weight Range of Common GumsGUMAVERAGE MOLECULAR WEIGHTOat β (1-3) β (1-4) glucan 500,000-1,000,000Pullulan50,000-100,000Curdlan ~500,000Methyl cellulose10,000-200,000Carrageenan4,500,000Xanthan15,000,000-50,000,000 Sodium alginate  10,000-18,000,000
Viscosity of a 1% solution of different polysaccharide gum solutions varies with origin and thus chemical nature. Table 2 shows the viscosity of 1% solutions of typical gums.
TABLE 2Typical Viscosity Ranges of 1% Solutionsof Common Gums, Measured at 25° C.GUMS1% SOLUTION VISCOSITY, cPOat β (1-3) β (1-4) glucan 500-1000Pullulan 2Gum arabic1-5Methyl cellulose200Tamarind gum100-200Guar gum2,000-3,000Locust bean gum2,000-3,000Xanthan2,000-3,000Sodium alginate200-700
High viscosity and solution pouring effects are undesirable in pouring films and in mixing formulations. Typically heat >50° C. is required to ensure fluidity in mixing and pouring. The high viscosity of native β(1-3) β(1-4) glucan teaches away from the use of these materials in the preparation of films.
The solubility properties of glucans differ according to their source. For example cereal β(1-3) β(1-4) glucans are normally soluble in aqueous solvents, whereas yeast (Saccharomyces cerevisiae) β(1-3) β(1-6) are insoluble in aqueous solvents. Soluble glucans are desirable. Yeast beta glucan has been solubilized by the addition of phosphate groups (see Williams et al. Immunopharmacol. 22: 139-156 (1991)0. Jamas et al. (U.S. Pat. No. 5,622,939) describes methods to extract soluble beta glucan from Saccharomyces cerevisiae. The method described is complex involving acid hydrolysis, base hydrolysis and the extensive use of centrifugation and ultrafiltration. No details are provided as to the stability of the solubilized yeast β(1-3) β(1-6) glucan.
Beta glucans affect the viscosity and hence the effectiveness of products derived from these sources. For example, beta glucans appear to influence digestion, assist in glucoregulation, and lower serum cholesterol. Cereal beta glucans are useful nutritional agents and have also been used as bulking agents in place of sucrose. Beta glucans have also been described as potent immune system stimulants and promote the healing of wounds (Yun et al. Int. J. Parasitol. (1997) 27:329-337; Estrada et al (1997)). The immune stimulatory activity of oat β(1-3) β(1-4) glucan is described by Estrada et at (1997, Microbiol. Immunol. 41:991-998). Differences in immune stimulation between β glucans from different sources are described.
Williams et al. (U.S. Pat. No. 5,676,967) describe a wound healing gauze for use in skin loss injuries and burns. The gauze described presents a combination oat β(1-3) β(1-4) glucan and collagen presented on a rigid support mesh. Self-supporting films of β(1-3) β(1-4) are not described.
Cereal β(1-3) β(1-4) glucan has also been used as a suspending solution for biocompatible particles for tissue injection (Lawin et al. U.S. Pat. No. 5,451,406).
Redmond (U.S. Pat. No. 6,284,886) describes methods and compositions of solutions of cereal β(1-3) β(1-4) glucan. The described compositions meet the restricted requirements of cosmetics industry which favours the use of beta glucan for its viscosity, shear strength, and moisture enhancing properties. No film or dry glucan preparations are described.
U.S. Pat. No. 6,323,338 discloses a method of isolating oat beta glucan as an enriched skin from an extract of oat bran. This reference does not disclose films comprising cereal beta glucan and a compound of interest, or a method of formulating these films.
There are a number of disclosures on the use of thin films made from a variety of polysaccharide material. These prior art references include for example: Japanese applications JP 5-236885 and JP 5-1198; U.S. Pat. Nos. 5,518,902; 5,411,945; 4,851,394; 3,784,390; 4,623,394 and International PCT publications WO 99/17753; WO 98/26780; WO 98/20862; WO 98/26763 and WO 00/18365. These prior art thin film products can also include a variety of ingredients, for example antibacterial agents, flavouring agents, other polysaccharides and pharmaceutically active substances.
According to the present invention it has been found that the use of cereal β(1-3) β(1-4) glucan was advantageous in comparison with other gums since it formulates at lower percentages and surprisingly thin films are more easily formed with either no need for or reduced need for other gums in the finished formulation. Central to the present invention is the surprising ability of β(1-3) β(1-4) glucan to sequester hydrophobic materials and alcoholic extracts. This capacity lends itself to the remarkable oil carrying ratios of cereal β(1-3) β(1-4) glucan.
Edible films to date have been manufactured from lower molecular weight gums since the higher molecular weight gums typically have a high viscosity of solution which makes thin films difficult to obtain. The advantage of using oat beta glucan is that lower percentages of gel can be used in film formation. Further, with these lower percentages, the material may be poured cool which has a protective effect on associated materials such as volatile oils and pharmaceutical compounds which may be temperature sensitive.